You might find some of the NRC's comments on I-131 therapy patient release
interesting. Below I have reproduced part of the jan. 29, 1997 NRC Fed Reg
notice. You can get the whole thing from the GPO Web
page.
Partial answers to your questions are:
1. No. There are many kind of I-131 therapy/scans. 5 mCi doses are
common for scans, 30 mCi doses are
used to treat hyperthyroid disease and as an ablative dose following removal
of a cancerous thyroid. High
dose I-131 therapy patients (usually 100 - 200 mCi dose) are not released
until the amount of I-131 remaining
is 30 mCi or less and the dose rate is < 5 mR/hr @ 1m (current rules). So
the patient will be release with
30 mCi _or less_ depending on the treatment.
2 & 3 See NRC comment & response below. The most significant source of
contamination for high dose
patients while they are hospitalized is definately through the urine - most
of the iodine is excreted fairly
quickly. However, all body fluids will have some contamination potential,
but usually not very significant.
4 With high dose I-131 therapy patients, we see an effective half-life
of about 1 day (or less) for
the first couple of days. I.e., a patient given 100 mCi will be at about 50
mCi 24 hours later. Since we release patients when they have 30 mCi, we
have little experience with the long term retention, but we
presume that after a few days the effective hal-life begins to approach the
radioactive half-life, as the
retained iodine is strongly retained.
5. Most patients are released to go back to jobs where they have no
radiological equipment/expertise/problems/worrys/neuroses. These people do
just fine. You might want to check the thyroids
of your techs before & after.
Hope this helps.
_____________________________________________________________________
Reproduced from 62 FR 4123
Comment. Several commenters said that the release of patients with
more than 30 millicuries of iodine-131 should not be permitted because
of concerns about the risk of internal exposure. One commenter said
that doses to family members from the patient vomiting were not
adequately considered. The same commenter also said that a study
indicated that in-home contamination by patients dosed with I-131 could
double family members' risk of developing thyroid cancer.
Response. The concern over contamination is not justified by the
radiation doses that are likely to be caused by the removal of
radionuclides from the patient's body by the pathways of exhaled air,
feces, saliva, sweat, urine, and vomit. Measurements from several
studies, as discussed in the supporting regulatory analysis, have shown
that a relatively small proportion of the radioactive material
administered will appear as contamination. Doses to family members
exposed to contamination from living in close contact with released
patients have been measured in several studies and in every case were
less than 10 percent of the 5-millisievert (0.5-rem) total effective
dose equivalent limit and were most often less than 1 percent of the 5-
millisievert (0.5-rem) limit. In addition, the internal doses resulting
from contamination were always less and generally far less than the
external dose, meaning that contamination was the less important source
of radiation exposure. These measurements show that even if the family
members repeatedly touched household items touched by the patient,
contamination does not cause unacceptably high doses. These findings
were true even in the case of a British study where eleven patients
volunteered to disregard special precautions against contamination and
minimizing spousal and family exposure. These measurements are
discussed in NUREG-1492. Also, the NCRP recently addressed the risk of
intake of radionuclides from patients' secretions and excreta in NCRP
Commentary No. 11, ``Dose Limits for Individuals Who Receive Exposure
from Radionuclide Therapy Patients,'' and concluded that, ``* * * a
contamination incident that could lead to a significant intake of
radioactive material is very unlikely.'' <SUP>2
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\2\ National Council on Radiation Protection and Measurements,
``Dose Limits for Individuals Who Receive Exposure from Radionuclide
Therapy Patients,'' NCRP Commentary No. 11 (February 28, 1995).
(Available for sale from the NCRP, 7910 Woodmont Avenue, Suite 800,
Bethesda, MD 20814-3095.)
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In general, the physical reactions (e.g., vomiting) that a patient
may experience from the administration of any radiopharmaceutical are
rare. Vomiting is seldom an important elimination route for
radiopharmaceuticals after the patient has left the medical facility
since orally administered radiopharmaceuticals such as iodine-131 are
rapidly absorbed, within a half hour, by the gastrointestinal system.
Regarding the comment on the doubling of risk of developing thyroid
cancer, there is no scientific consensus by the United Nations
Scientific Committee on the Effects of Atomic Radiation, ICRP, or NCRP
to support the suggested increased risk of thyroid cancer following
ingestion of iodine-131. Based on the information currently available,
the Commission continues to conclude that the benefits outweigh the
potential of small increased risks associated with this rule.
Don Jordan
The University of Chicago
Office of Radiation Safety
Zoology Building Room 11
1101 East 57th Street
Chicago, Illinois 60615
Tel. 773-702-6299
Fax 773-702-4008
email Don_Jordan@fpm.uchicago.edu